<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>

<button id = 'btn'>点击</button>

<script>
    var btn = document.getElementById('btn');
    btn.addEventListener('click', fn);
    btn.addEventListener('dblclick', fn1);
    function fn() {
        alert('2班')
        btn.removeEventListener('click',fn)
    }
    function fn1() {
        alert('4班');
    }

</script>
</body>

</html>